Press brake tooling comprises a punch having an elongated edge which is generally "V" shaped in cross section, and a die having an elongated groove which has a complementary V-shaped cross sectional configuration. The upwardly open V-shaped groove of the die terminates upwardly in a pair of spaced edges. When a work piece--a piece of sheet metal, for example, is to be bent in the press brake, it is placed between the punch and the die, and the punch , which is vertically aligned with the die, presses downwardly upon the work piece. As the work piece bends, its bottom edges slide across the spaced edge surfaces of the groove. As this occurs, the edge surfaces of the groove may become scratched, chipped or otherwise worn away. The V-shaped punch, on the other hand, has a downwardly facing edge that contacts the upper surface of the workpiece primarily at a single line of contact, and comparatively little sliding motion between the workpiece and the punch edge occurs.
Depending upon the character of the surface of the work piece, and its stiffness (that is, its resistance to bending), the sliding motion between the bottom surface of the work piece and the surfaces of the spaced edges of the die can cause substantial damage to the spaced edges of the die. Once scratches, pits or wear appear in the die, the rate of wear of the die accelerates, and when the die surface is damaged to the point that the workpiece is affected, of course, the die must be replaced.
For reasons of economy, it is important that a die be capable of being used many times before the die needs to be replaced. To this end, die surfaces have been hardened so as to resist scratching, pitting or wear. The hardening of these surfaces, due to the methods of hardening, has been continued deep into the surfaces.
Two basic methods have been used to harden the surfaces of press brake dies. One of these methods involves making the entire die out of a tempered steel piece, but the resulting die is susceptible to breakage during use. The second method involves a heat hardening method, such as flame hardening or induction hardening, in which the surfaces of the die are hardened generally down to a depth of 1/8" or more in order to achieve the desired surface hardness. This is a somewhat long and expensive process and produces only fair results.
As mentioned above, the hardening processes commonly used continue the hardening process well into the thickness of the die from its surface. Accordingly, die hardening methods involving only surface hardening, for example, have not been thought adequate.
It would be desirable to provide a die having a edge surfaces that are so resistant to abrasion as to be capable of repeated use without significant scratching, pitting or wear, thus reducing the necessity of purchasing expensive tooling and reducing downtime as dies are replaced.